Done that.
Additionally the user guide says that daisy chaining hubs is not supported.
Obviously I don't know whether it will always work but is has worked for me when using both ports and no hub on the few occasions I did that back before I installed the CF.I think it depends on the format of the USB drives, but copying from one usb drive to another might not work: it may not distinguish between the drives and try to move rather than copy the files.